The introduction of air into the vascular system is a potential complication of many procedures involving infusion of blood or other fluids. Air bubbles entrained in the infused fluid can cause air emboli, with potentially fatal consequences. In patients who undergo repeated infusion in large volumes, such as kidney failure patients being treated by hemodialysis, even small concentrations of air in the infused fluid can have serious cumulative effects. Although modern dialysis machines generally include a bubble trap, small bubbles may still penetrate therethrough into the blood being re-infused.
Various methods and devices are known in the art for eliminating air bubbles from blood. For example, PCT International Publication WO 01/41655, whose disclosure is incorporated herein by reference, describes a device that uses ultrasonic energy to cause microbubbles in a stream of liquid to be concentrated in a particular area of the flow (such as the center or one side of a tube carrying the liquid flow). A downstream vent tube then removes these bubbles into a sidestream, which is directed to a filter.
As another example, U.S. patent Application Publication US 2005/0192525, the disclosure of which is incorporated herein by reference, describes a system for removing gas bubbles from blood during circulatory assist procedures. In an active filter, the bubbles are forced to the center of a disposable filter chamber and are thereby removed from the blood before it reaches a peripheral exit from the filter. Inside the filter, a rotatable impeller with a magnetic coupler is driven by an external magnetic driver, spinning the blood and thus causing the lower density bubbles to move toward the central of the blood filter by centripetal force. The bubbles collect in a gas trap, from which the gas is bled off through a bleed valve. Other systems for removing gas from blood using a magnetically-driven impeller are described in U.S. Pat. Nos. 6,730,267, 6,773,670 and 6,960,322, whose disclosures are also incorporated herein by reference.
Other devices for removing gas bubbles from flowing blood have used a cyclone device, without moving parts, to cause the blood to flow in a helical path. Such devices are described, for example, in U.S. Pat. Nos. 5,824,212 and 6,053,967, whose disclosures are incorporated herein by reference. The rotating cyclone stream causes the air to be forced into the radial center of the stream, where it may be separated from the liquid.